Specifies which I/O event dispatcher to use. Different operating systems support different types of event dispatcher:

Linux kernel 2.4.x supports:

poll

Linux kernel 2.6.x supports:

poll

epoll

FreeBSD supports:

poll

kqueue

Solaris supports:

poll

devpoll

Mac OS X 10.3 and above supports:

poll

kqueue

poll is supported by all platforms, and is the default selection. For high traffic web sites, an altenative event dispatcher can be used to improve the scalability of the server.

Syntax

Select from drop down list

Default SHM Directory

Description

Changes shared memory's default directory to the specified path. If the directory does not exist, it will be created. All SHM data will be stored in this directory unless otherwise specified.

Syntax

Path

Max Connections

Description

Specifies the maximum number of concurrent connections that the server can accept. This includes both plain TCP connections and SSL connections. Once the maximum concurrent connections limit is reached, the server will close Keep-Alive connections when they complete active requests.

Syntax

Integer number

Tips

When the server is started by "root" user, the server will try to adjust the per-process file descriptor limits automatically, however, if this fails, you may need to increase this limit manually.

Max SSL Connections

Description

Specifies the maximum number of concurrent SSL connections the server will accept. Since total concurrent SSL and non-SSL connections cannot exceed the limit specified by Max Connections, the actual number of concurrent SSL connections allowed must be lower than this limit.

Syntax

Integer number

Connection Timeout (secs)

Description

Specifies the maximum connection idle time allowed during processing one request. The connection will be closed if it has been idle, i.e. no I/O activity, for this period of time.

Syntax

Integer number

Tips

[Security] Set this as low as you can to help recover dead connections during a potential DoS attack.

Specifies the maximum number of requests that can be served through a keep-alive (persistent) session. The connection will be closed once this limit is reached. You can set this limit for each virtual host as well.

Syntax

Integer number

Tips

[Performance] Set this to a reasonably high value. A value of "1" or "0" will disable keep-alive.

Specifies whether to turn on Smart Keep-Alive. This option is effective only if Max Keep-Alive Requests is greater than 1. If enabled, you can also enable/disable it at the virtual host level. Smart keep-alive will only establish keep-alive connections for requests of JavaScript, CSS Style Sheet, and image files. For html pages, the connection will not be kept alive. This will help serve more users more efficiently. Normally a web page contains multiple images and scripts that will be cached by the browser after the initial request. It is more efficient to send those non-html static files through a single keep-alive connection and have the text/html file sent through another non-keep-alive connection. This method will reduce idle connections and in turn increase the capacity to handle more concurrent requests and users.

Specifies the maximum idle time between requests from a keep-alive connection. If no new request is received during this period of time, the connection will be closed. This setting only applies to HTTP/1.1 connections. HTTP/2 connections have long keep-alive timeouts by design and are not affected by this setting.

Syntax

Integer number

Tips

[Security & Performance] We recommend that you set this value just long enough to wait for subsequent requests from a client when there are more assets referenced by a single page that need to be loaded. Do not set this too long hoping that the next page will be served over the keep-alive connection. Keeping many idle keep-alive connections is a waste of server resources and could be taken advantage of by (D)DoS attacks. 2-5 seconds is a reasonable range for most applications. LiteSpeed is highly efficient in a non-keep-alive environment.

Send Buffer Size (bytes)

Description

The sending buffer size of each TCP socket. 512K is the maximum allowed buffer size.

Syntax

Integer number

Tips

[Performance] It is recommended to leave this value as "Not Set" or set to 0 to use the operating system's default buffer size. [Performance] If your web site serves large static files, increase the send buffer size to improve performance. [Performance] Setting this to a lower value will reduce throughput and memory usage per socket allowing the server to have more concurrent sockets when memory is a bottleneck.

Receive Buffer Size (bytes)

Description

The receiving buffer size of each TCP socket. 512K is the maximum allowed buffer size.

Syntax

Integer number

Tips

[Performance] It is recommended to leave this value as "Not Set" or set to 0 to use the operating system's default buffer size. [Performance] A large receive buffer will increase performance when processing incoming requests with large payloads, i.e. file uploads. [Performance] Setting this to a lower value will reduce throughput and memory usage per socket allowing the server to have more concurrent sockets when memory is a bottleneck.

Max Request URL Length (bytes)

Description

Specifies the maximum size of a request URL. URL is the full text address used to access a server resource including the query string. 8192 bytes is the hard limit.

Syntax

Integer number

Tips

[Security & Performance] Set it reasonably low to reduce memory usage and help identify bogus requests and DoS attacks. 2-3K is big enough for most web sites unless the HTTP GET method is used with large query strings instead of POST.

[Reliability & Performance] Set the limit reasonably low to help identify bad responses. It is not uncommon to malformed scripts to contain an infinite loop which leads to infinity-sized responses.

Max Cached Small File Size (bytes)

Description

Specifies the largest static file that will be cached in a pre-allocated memory buffer. Static files can be served in four different ways: memory buffer cache, memory-mapped cache, plain read/write, and sendfile(). Files whose size is smaller than this setting are served from memory buffer cache. Files whose size is larger than this setting, but smaller than the Max MMAP File Size (bytes) will be served from memory-mapped cache. Files whose size is larger than the Max MMAP File Size (bytes) will be served via plain read/write or sendfile(). It is optimal to serve static files smaller than 4K from the memory buffer cache.

Syntax

Integer number

Total Small File Cache Size (bytes)

Description

Specifies the total memory that can be allocated to the buffer cache in order to cache/serve small static files.

Syntax

Integer number

Max MMAP File Size (bytes)

Description

Specifies the largest static file that will be memory mapped (MMAP). Static files can be served in four different ways: memory buffer cache, memory-mapped cache, plain read/write, and sendfile(). Files whose size is smaller than the Max Cached Small File Size (bytes) are served from memory buffer cache. Files whose size is larger than the Max Cached Small File Size (bytes), but smaller than the Max MMAP File Size will be served from memory-mapped cache. Files whose size is larger than the Max MMAP File Size will be served via plain read/write or sendfile(). Since the server has a 32bit address space (2GB), it is not recommended to memory map very large files.

Syntax

Integer number

Total MMAP Cache Size (bytes)

Description

Specifies the total memory that can be allocated for memory- mapped cache in order to cache/serve medium sized static files.

Syntax

Integer number

Use sendfile()

Description

Specifies whether to use the sendfile() system call to serve static files. Static files can be served in four different ways: memory buffer cache, memory-mapped cache, plain read/write, and sendfile(). Files smaller than the Max Cached Small File Size (bytes) are served from memory buffer cache. Files larger than the Max Cached Small File Size (bytes) but smaller than the Max MMAP File Size (bytes) will be served from memory-mapped cache. Files larger than the Max MMAP File Size (bytes) will be served via plain read/write or sendfile(). Sendfile() is a "zero copy" system call that can greatly reduce CPU utilization when serving very large static files. Sendfile() requires an optimized network card kernel driver and thus may not be suitable for some small-vendor network adapters.

Syntax

Select from radio box

File ETag

Description

Specifies whether to use a file's inode, last-modified time, and size attributes to generate the ETag HTTP response header for static files. All three attributes are enabled by default. If you plan to serve the same file out of mirrored servers, you should not include inode; otherwise, the ETag generated for one file will be different on different servers.

Syntax

Select from checkbox

Enable Compression

Description

Controls GZIP compression for both static and dynamic HTTP responses.

Syntax

Select from radio box

Tips

[Performance] Enable it to save network bandwidth. Text-based responses such as html, css, and javascript files benefit the most and on average can be compressed to half of their original size.

Enable Dynamic Compression

Description

Controls GZIP compression for dynamically generated HTTP response. Enable Compression must be set to Yes in order to enable dynamic GZIP compression.

Specifies the level of compression for dynamic content. Ranges from 1 (lowest) to 9 (highest). The default is 2.

Syntax

Number between 1 and 9.

Tips

[Performance] Higher compression level will use more memory and CPU cycles. You can set it to a higher level if your machine has additional power. There is not much difference between 6 and 9, except 9 uses many more CPU cycles.

If you want to compress text/* but not text/css, you can have a rule like text/*, !text/css. "!" will exclude that MIME type.

Tips

[Performance] Only allow types that will benefit from GZIP compression. Binary files such as gif/png/jpeg images and flash files do not benefit from compression.

Auto Update Static File

Description

Specifies whether to let the server automatically create/update GZIP-compressed versions of compressible static files or not. If set to Yes, when a file with a MIME type listed in Compressible Types is requested, the server may create or update the corresponding compressed version of the file depending on the compressed file's timestamp. This compressed file is created under the Static GZIP Cache Directory. The filename is based on a MD5 hash of the path of the original file.

Syntax

Select from radio box

Static GZIP Cache Directory

Description

Specifies the path of the directory used to store compressed files for static content. The default is Swapping Directory.

Syntax

Directory Path

Compression Level (Static Content)

Description

Specifies the level of compression for static content. Ranges from 1 (lowest) to 9 (highest). The default is 6.

Syntax

Number between 1 and 9.

Max Static File Size (bytes)

Description

Specifies the maximum size of a static file for which the server will create a compressed file automatically.

Syntax

Number in bytes not less than 1K.

Tips

[Performance] It is not recommended to have the server create/update compressed files for large files. Compressing blocks an entire server process and no further requests can be processed until the compression is completed.

Min Static File Size (bytes)

Description

Specifies the minimum size of a static file for which the server will create a corresponding compressed file.

Syntax

Number in bytes not less than 200.

Tips

It is not necessary to compress very small files as the bandwidth saving is negligible.

SSL Strong DH Key

Description

Specifies whether to use 2048 or 1024 bit DH keys for SSL handshakes. If set to "Yes", 2048 bit DH keys will be used for 2048 bit SSL keys and certificates. 1024 bit DH keys will still be used in other situations. Default is "Yes".

Earlier versions of Java do not support DH key size higher than 1024 bits. If Java client compatibility is required, this should be set to "No".

Syntax

radio

Enable Multiple SSL Certificates

Description

Allows listeners/vhosts to set multiple SSL certificates. If multiple certificates are enabled, the certificates/keys are expected to follow a naming scheme. If the cert is named server.crt, other possible cert names are server.crt.rsa, server.crt.dsa, server.crt.ecc. If "Not Set", defaults to "No".